Studies of the cardiovascular components of the reflex response will be performed in newborn lambs. Chronic preparations with implanted electromagnetic flowcuffs will be used in conjunction with microsphere injections in order to evaluate redistribution of the blood flow to different organs. Ways to block the respiratory, as well as the cardiovascular, reflex response will be explored in the lambs. Further studies are planned in newborn lambs of the damaging effect of acid solutions on the laryngeal epithelium. A correlation between histopathological findings, the chemoreflex function and the occurrence of aspiration during feedings will be attempted. Continued reflex studies of premature infants with unexplained recurrent apnea will be undertaken in order to identify infants who have reflex apnea as a laryngeal chemoreflex response. Blood samples from preterm infants will be analyzed for copper and zinc. Infants receiving intravenous feedings with added zinc and copper will have serum zinc and copper measurements made in an effort to determine any benefit from such supplementation. Post mortem tissues of infants who die during the first two months of life will be collected for the purpose of comparing serum and tissue concentrations of copper and zinc. The laryngeal chemoreflex will be tested in infants with respiratory failure, in whom trace element levels are shown to be low, before and after repletion of trace element levels.